Rigid polyurethane foam-forming compositions

ABSTRACT

Advantageous rigid polyurethane foam properties (e.g. compressive strength) can be improved and the proportions of polymerization catalyst and/or surfactant needed to provide a given level of such properties can be lowered by preparing such foams from compositions comprising, in addition to the conventional foam-forming reactants including polyisocyanate and polyol, from about 3% to about 10%, based on the weight of the polyol, of a plasticizer selected from essentially halogen-free phosphates and carboxylates containing at least one aryl radical, e.g. isodecyl diphenyl phosphate or butyl benzyl phthalate.

BACKGROUND OF THE INVENTION

Production of various kinds of rigid polyurethane foam is known in the art. Such production is typically carried out by subjecting a mixture of organic polyisocyanate and polyol having more than two hydroxy radicals per molecule to polyurethane foam-forming reaction conditions. Usually the reaction is catalyzed, e.g. by including an amine or tin compound in the reaction mixture. Also typically included in the mixture are secondary blowing agents (e.g. Freon) to lower the density and surfactants (e.g. silicones) to improve the uniformity of the resulting foam. Such catalysts, surfactants and blowing agents are normally added in relatively small proportions, but they are expensive. Hence the quantities in which they must be used have a significant impact on manufacturing cost of the foam.

Accordingly, it would be very advantageous if significant properties of the foam could be improved without need for more of such expensive constituents of the polymerization mixture, or if foams of equivalent properties could be produced while using smaller quantities of such constituents. An object of this invention is a rigid polyurethane foam-forming composition which provides those advantages. Another object is to provide the rigid polyurethane foams produced therewith. Other objects of this invention will be apparent from the following in which, except where otherwise noted, percentages are by weight and temperatures are Celsius.

SUMMARY OF THE INVENTION

In accordance with this invention, the aforesaid advantages are provided by use of a rigid polyurethane foam-forming composition comprising an organic isocyanate, a polyol having more than two hydroxy radicals per molecule and, based on the weight of said polyol, from about 3% to about 10% of a plasticizer selected from essentially halogen-free phosphates and carboxylates containing at least one aryl radical. Also provided by this invention are the rigid polyurethane foams produced by subjecting such compositions to polyurethane foam-forming reaction conditions.

DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, polyurethane foam-forming reactants means polyurethane monomers capable of polymerizing by urethane linkage-forming reactions. Preferably such reactants have not yet undergone substantial polymerization to the extent of forming polyurethane "prepolymer", e.g. as disclosed in U.S. Pat. No. 3,975,316 issued Aug. 17, 1976 to J. L. Villa. Also preferably, the foam-forming compositions of this invention contain essentially no reactants (other than said polyurethane foam-forming reactants) which polymerize substantially under conventional polyurethane foam-forming polymerization conditions.

As aforesaid, this invention is carried out using conventional rigid polyurethane foam-forming reactants including an organic polyisocyanate and a polyol having more than two hydroxy radicals per molecule. Preferred examples of such reactants are polymethylene polyphenyl isocyanates such as 4,4'-diphenylmethane diisocyanate and a castor oil- or sucrose-based hydroxyl-terminated polyhydric polymeric material, respectively. Catalysts which may be used to control the rate of the polymerization of such reactants include various tertiary amines such as, e.g. trialkylamines (hydroxylated or non-hydroxylated) and morpholines, and various tin compounds such as, e.g. stannous oxalate or dibutyl tin oxide. To improve the uniformity of the foam, it has been conventional to include in the reaction mixture a surfactant, normally of the silicone variety, e.g. poly(dialkyl siloxane)s or a silicone-glycol. Blowing agents (e.g. Freon) are typically employed to lower foam density. Also employed in production of the foams of this invention are conventional polyurethane foam-forming reaction conditions which normally include uniform mixing of the urethane-forming reactants and then allowing their exothermic reaction to begin at approximately room temperature and proceed to a desired degree of completion. Commonly the proportion of isocyanate to polyol is varied to achieve a desired relationship between product foam stability and manufacturing cost. Generally such foam stability is better when the NCO/OH Index (theoretical stoichiometric ratio of the isocyanate to the polyol and water present in the reaction mixture and capable of reacting with that isocyanate) is at least about 100 and, usually even more desirably, at least about 103. Further details and numerous additional examples of conventional rigid polyurethane foam-forming reactants, catalysts, surfactants, blowing agents and reaction conditions can be found in the published literature including, e.g. "Polyurethanes--Chemistry and Technology", J. H. Saunders and K. C. Frisch, Interscience Publishers, Division of John Wiley & Sons, Parts I & II (1962 & 1964); "Plastic Foams" edited by K. C. Frisch and J. H. Saunders, Marcel Dekker, Inc., Parts I & II (1972 & 1973); The Development and Use of Polyurethane Products, E. N. Doyle, MacGraw-Hill Book Co. (1971); A Glossary of Urethane Industry Terms, S. Alan Stewart, The Martin Sweets Co., Inc. Louisville, Ky. (1971); and "The Chemistry of Silicone Surfactants for Urethane Foams", R. M. Bryant et al., Journal of Cellular Plastics 99 (March/April 1973).

As aforesaid, the plasticizer used in this invention is essentially halogen-free and selected from phosphates and carboxylates containing at least one aryl radical per molecule. Such phosphates can be triaryl phosphates, such as, e.g. isopropylphenyl diphenyl phosphate, t-butyl-phenyl diphenyl phosphate, tricresyl phosphate or triphenyl phosphate; alkyl diaryl phosphates such as, e.g. C₉ -C₁₁ alkyl diphenyl phosphate, isodecyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, isooctyl diphenyl phosphate, C₇ -C₉ alkyl diphenyl phosphate, or isononyl dicresyl phosphate; or dialkyl aryl phosphates such as, e.g. di-isodecyl phenyl phosphate, di-isododecyl t-butyl-phenyl phosphate or di-undecyl cresyl phosphate. Preferred among those phosphates are the alkyl diaryl phosphates, particularly isodecyl diphenyl phosphate, and the triaryl phosphates, particularly t-butyl-phenyl diphenyl phosphate. The carboxylate plasticizers useful in this invention may contain an aryl radical on either or both sides of a carboxyl radical, e.g. dialkyl phthalates, diaryl adipates or benzyl phthalates. Preferred are dicarboxylates such as, e.g. phthalates, terephthalates, isophthalates, adipates, glutarates, sebacates, pimelates, azelates, succinates, etc., although mono-carboxylates such as benzyl stearate, etc. are also useful. Most preferred are the phthalates, including dialkyl phthalates in which the average carbon atom content per alkyl radical is between about 6 and about 12 (e.g. dioctyl phthalate), diaryl phthalates such as dibenzyl phthalate, and most advantageously for many uses, alkyl aryl phthalates such as butyl benzyl phthalate, octyl benzyl phthalate, texanol (e.g. 2,2,4-trimethylpentyl) benzyl phthalates, etc. Also attractively useful herein are isophthalates and terephthalates such as, e.g. bis(2-ethylhexyl)terephthalate. Preferred among the dicarboxylates of aliphatic dicarboxylic acids are diaryl dicarboxylates such as, e.g. dibenzyl adipate, dicresyl sebacate, etc.

As aforesaid, advantageous foam properties and/or lowered requirements for reaction mixture constituents such as polymerization catalysts, surfactants and/or blowing agents are provided when the compositions of this invention contain from about 3% to about 10% of such a plasticizer, based on the weight of polyol in that composition. In most instances, even more advantageous results are obtained when the composition contains not less than about 4% and not more than about 8.5% of the plasticizer, based on the weight of that polyol, and in many instances most advantageous results are obtained when the composition contains not less than about 5 and not more than about 7% of the plasticizer, based on the weight of that polyol. Preferably the plasticizer is essentially uniformyl dispersed (e.g. by any conventional means) throughout the foam-forming composition employed in this invention.

The following are specific examples of foam-forming compositions and rigid polyurethane foams produced therefrom in accordance with this invention. These examples are illustrative only and do not imply any limitations on the scope of the invention.

EXAMPLE I

Various rigid polyurethane foam-forming compositions were prepared by mixing 100 parts of a moderate-viscosity, sucrose-based polyol having a hydroxyl number of 470 mg KOH/gm with a polymethylene polyphenyl isocyanate having an NCO content of 31.5% and an amine equivalent of 132, 3 parts of a polymerization catalyst blend composed of 80% dimethylethanolamine and 20% of triethylenediamine, 1.6 parts of a low-viscosity silicone-glycol copolymer surfactant having a viscosity of 465 cs at 25°, 35 parts of Freon and zero or one part of distilled water. Separate batches were made using different proportions of the isocyanate such that they had NCO/OH Indices (defined hereinbefore) of 96, 108 and 120. In two duplicate sets of such compositions, 5 parts and 10 parts, respectively, of butyl benzyl phthalate were also included. The foam-forming compositions were then thoroughly mixed and subjected to conventional polyurethane-forming reaction conditions beginning at room temperature. Each resulting rigid foam was subjected to measurements of density and compression load deflection (hereinafter CLD) by ASTM D-1564-64. Average results were as follows:

                                      TABLE A                                      __________________________________________________________________________     Parts of                                                                             Index 96          Index 108         Index 120                            Butyl CLD.sup.1                                                                              Density.sup.2                                                                            CLD.sup.1                                                                              Density.sup.2                                                                            CLD.sup.1                                                                              Density.sup.2                Benzyl                                                                               No      No        No      No        No      No                           Phthalate                                                                            H.sub.2 O                                                                          H.sub.2 O                                                                          H.sub.2 O                                                                           H.sub.2 O                                                                           H.sub.2 O                                                                          H.sub.2 O                                                                          H.sub.2 O                                                                           H.sub.2 O                                                                           H.sub.2 O                                                                          H.sub.2 O                                                                          H.sub.2 O                                                                           H.sub.2 O               __________________________________________________________________________     None  0.77                                                                               1.15                                                                               0.027                                                                               0.024                                                                               0.92                                                                               1.22                                                                               0.029                                                                               0.024                                                                               0.90                                                                               1.27                                                                               0.029                                                                               0.026                   5     1.60                                                                               1.13                                                                               0.035                                                                               0.024                                                                               2.20                                                                               1.24                                                                               0.037                                                                               0.025                                                                               2.33                                                                               1.29                                                                               0.039                                                                               0.026                   10    0.96                                                                               1.12                                                                               0.037                                                                               0.026                                                                               2.35                                                                               1.21                                                                               0.039                                                                               0.026                                                                               2.48                                                                               1.29                                                                               0.041                                                                               0.027                   __________________________________________________________________________      .sup.1 kg/cm.sup.2                                                             .sup.2 g/cc                                                              

From Table A it can be seen that particularly at NCO/OH Indices of 108 and 120, the foams made using compositions containing 5 and 10 parts of butyl benzyl phthalate have substantially higher CLD than the corresponding foams made without inclusion of that plasticizer.

EXAMPLE II

Additional runs were carried out varying the concentrations of amine and butyl benzyl phthalate in foam-forming compositions otherwise like those of Example I having as NCO/OH Index of 108 and containing one part of distilled water. Results were as follows:

                                      TABLE B                                      __________________________________________________________________________     Parts of                                                                       Butyl                                                                          Benzyl                                                                               CLD, kg/cm.sup.2    Density g/cc                                         Phthalate                                                                            0   3   5   7   10  0    3    5    7    10                               __________________________________________________________________________     3 parts of                                                                     the amine                                                                            1.22                                                                               1.13                                                                               1.25                                                                               1.43                                                                               1.42                                                                               0.026                                                                               0.026                                                                               0.027                                                                               0.027                                                                               0.027                            2 parts of                                                                     the amine                                                                            1.27                                                                               0.85                                                                               1.30                                                                               1.28                                                                               1.20                                                                               0.027                                                                               0.026                                                                               0.027                                                                               0.027                                                                               0.027                            __________________________________________________________________________

From Table B it can be seen that (1) decreasing the parts of amine increases the density of foams made without the butyl benzyl phthalate but shows essentially no effect on the foams made using 3-10 parts of butyl benzyl phthalate and (2) with increasing parts of butyl benzyl phthalate, the CLD increases from 3 parts to a maximum using less than 10 parts thereof.

EXAMPLE III

Additional runs were carried out including butyl benzyl phthalate (10 parts) in foam-forming compositions like those of Example I containing one part water and having an NCO/OH Index of 108 but with varying concentrations of the amine. Results were as follows:

                  TABLE C                                                          ______________________________________                                                3.0 parts Amine                                                                              4.5 parts Amine                                           Butyl Benzyl                                                                            CLD,      Density,  CLD,    Density,                                  Phthalate                                                                               kg/cm.sup.2                                                                              g/cc      kg/cm.sup.2                                                                            g/cc                                      ______________________________________                                         None     1.22      0.025     1.20    0.025                                     10       1.30      0.026     1.23    0.027                                     ______________________________________                                    

Table C shows that in the presence of the butyl benzyl phthalate, increased CLD can be obtained despite the use of less amine.

EXAMPLE IV

Additional runs were carried out including butyl benzyl phthalate (10 parts) in foam-forming compositions like those of Example I having an NCO/OH Index of 108 and containing one part water but with varying concentrations of the silicone. Results were as follows:

                  TABLE D                                                          ______________________________________                                         Parts of                                                                       Butyl                                                                          Benzyl                                                                         Phthalate                                                                             0       10      10    10    10    10                                    ______________________________________                                         Parts of                                                                       Silicone                                                                              1.6     1.6     1.0   0.5   0.2   0                                     CLD,   1.22    1.30    1.40  1.53  1.46  Collapsed                             kg/cm.sup.2                                                                    Density,                                                                              0.025   0.026   0.027 0.028 0.027 Collapsed                             g/cc                                                                           ______________________________________                                    

Table D shows that in the presence of the butyl benzyl phthalate, increased CLD can be obtained despite the use of less silicone. 

We claim:
 1. Rigid polyurethane foam produced by subjecting to polyurethane foam-forming reaction conditions a composition comprising rigid polyurethane foam-forming reactants including an organic polyisocyanate and a polyol having more than two hydroxy radicals per molecule and, based on the weight of said polyol, from about 3% to about 10% alkyl aryl phthalate.
 2. Foam of claim 1 wherein the phthalate is butyl benzyl phthalate.
 3. Foam of claim 1, said composition comprising a silicine surfactant or amine catalyst for the formation of said polyurethane.
 4. Foam of claim 3 wherein the phthalate is butyl benzyl phthalate.
 5. Foam of claim 1, said composition containing not less than about 4% and not more than about 8.5% of said phthalate, based on the weight of said polyol.
 6. Foam of claim 5 wherein the phthalate is butyl benzyl phthalate.
 7. Foam of claim 5, said composition comprising a silicone surfactant or amine catalyst for the formation of said polyurethane.
 8. Foam of claim 1, said composition containing not less than about 5% and not more than about 7% of said phthalate, based on the weight of said polyol.
 9. Foam of claim 8, said composition comprising a silicone surfactant or amine catalyst for the formation of said polyurethane.
 10. Foam of claim 9 wherein the phthalate is butyl benzyl phthalate. 